Not to start a flame war, but there is simply no such thing as a unidirectional audio cable using copper or silver as it's conductor.
It IS possible to introduce bias and selective resistance onto a conductor through active (powered) means, and, of course you, can manufacture semi-conducting materials to do all sorts of interesting things with current flow.
It IS possible to introduce bias and selective resistance onto a conductor through active (powered) means, and, of course you, can manufacture semi-conducting materials to do all sorts of interesting things with current flow.